The present invention relates systems for ultrasonic imaging of a jaw, methods of use thereof and coupling cushions suited for use in the mouth. Specifically the invention relates to systems which employ improved proe configurations which permit imaging of the mandible and maxilla and facilitate visualization of bone and nerve canals.
Diagnostic imaging of hard tissue has numerous practical uses in various medical fields. In the fields of Dentistry, Dental Surgery and Implantology, for example, X-ray and CT imaging are extensively used for imaging the human upper and lower jaws. However, such imaging techniques suffer from several significant disadvantages. In order to illustrate the deficiencies of current day techniques for imaging hard tissue, let us consider, for example, existing jaw imaging techniques used today in dental implant surgery.
In many mammals, including humans, the jaws (upper and lower) comprise several layers of tissue. FIG. 1 shows a high-level schematic sectional view of a human lower jaw, or mandible 30. The external layer of mandible 30 comprises the gum 32, or the mucoperiosteal tissue covering the jawbone. Beneath gum 32 is a layer of cortical (compact) bone 34, which is normally dense bone tissue. Beneath cortical bone 34 lies an area of trabecular bone 36, which is normally bone tissue softer than cortical bone. Within the area of trabecular bone and along the mandibular jaw, runs the mandibular canal 38 carrying the inferior alveolar nerve 39. Mandibular canal 38 is an elongated tubular cavity of varying density, usually comprising dense (cortical type bone) borders. In cases where dense borders are not present, mandibular canal 38 is a conduit within a sponge-like matrix. In the latter case, mandibular canal cavity 38 may be distinguished from the cavities of the trabecular environment 36 by the mandibular canal's regular shape, i.e. an elongated tubular cavity. All cavities inside the cross-section of mandible 30 are normally filled with fluids. The upper region of the mandible forms the alveolar ridge 40 in which teeth 42 are normally situated.
FIG. 2a shows a low-level schematic sectional view of mandible 30. As mentioned hereinabove, in a normal situation alveolar ridge 40 comprises sockets housing teeth 42. FIG. 2b shows a sectional view of mandible 30 after the loss of a tooth, for example, due to tooth extraction. It is well known that following the loss of a tooth, the residual socket in alveolar ridge 40 regenerates and fills with hard tissue. The procedure of replacing a tooth with an implant-supported prosthesis has become very common and widely used. The process of fixture (implant) placement entails exposing the bone (raising the mucoperiosteal flap), and drilling a receptive site for the fixture. FIG. 2c shows a sectional view of mandible 30 with a drill 70 drilling into the alveolar ridge 40. The common procedure prior to installation of a dental fixture involves, inter alia, drilling into the cortical 34 and trabecular 36 bone of mandible 30 using a drill 70, in order to prepare a socket in which a fixture will be anchored. If an implantologist drilling into mandible 30 is not aware of the topology and internal structure thereof (e.g. precise location of mandibular canal 38) then during the drilling procedure drill 70 may contact and damage mandibular canal 38 and inferior alveolar nerve 39 situated therein, or drill outside the bone boundaries. Such damage can ultimately lead to severe pain, hemorrhage and even local paralysis, among other undesired consequences. For this reason, it is widely acknowledged that an implantologist must obtain an internal image of the mandible prior to performing the implant surgery.
Similarly, when planning implant surgery on a human upper jaw, or maxilla, an implantologist will also need to obtain an internal image of the jaw. FIG. 3a shows a schematic sectional view of a maxilla 50. The maxilla comprises an external layer of gum 52, under which lies a layer of cortical bone 54, enclosing an area of trabecular bone 56. Under trabecular bone 56 lies another layer of cortical bone 58 which serves as the floor of the signal and\or nasal cavities 60. In a normal (healthy) maxilla, a tooth 62 is anchored in the cortical 54 and trabecular-56 bone. FIG. 3b shows a sectional view of maxilla 50 after the loss of tooth 62, for example, due to tooth extraction. When preparing a receptive site for a fixture in maxilla 50, the implantologist uses a drill 72 in order to drill a hole through the cortical 54 and trabecular 56 bone. However, if the implantologist is not aware of the internal structure and shape of the jawbone (e.g. the location of signal and/or nasal cavities 60), the implantologist may perforate and damage cortical floor 58. Such perforation may lead to a serious signal infection and hemorrhage, as well as other undesired consequences. It is therefore common practice to obtain an internal image of the maxilla prior to the implant surgery.
The most common technique currently used in Implantology for imaging the lower and\or upper jaw is Panoramic X-ray Radiography. FIG. 4 is an example of a panoramic x-ray image of human upper and lower jaws. In the lower jaw, mandibular canal 38 (black) appears inside trabecular bone area 36 (gray). A cortical bone layer 34 (white) encloses trabecular bone area 36. In the upper jaw, signal and nasal cavities 60 (black) appear above cortical floor 58 (white), which is above trabecular bone area 56 (gray), under which lies cortical bone layer 54 (white).
The panoramic X-ray technique suffers from some significant shortcomings. First, it is well established that X-ray radiation is hazardous to the health of the patient. Second, panoramic X-ray produces a two-dimensional image of the jaw, which is perpendicular to a cross-section of the jaw. This limitation makes the panoramic image unreliable for guiding the implantologist to drill within the bone boundaries and within a safe distance from the mandibular canal, or the signal\nasal cavities. The panoramic image is inherently distorted and inaccurate because it projects the three-dimensional jaw into a two-dimensional image. This image is therefore unreliable also for assessing the depth of the bone tissue available for drilling and preparing a fixture. Third, the image is not taken chair-side and consequently, panoramic X-ray does not allow for real-time monitoring of implant procedures. All of the above disadvantages make the panoramic X-ray image a hazardous, imprecise, and unreliable imaging solution.
Another imaging technique used in Implantology, though less common, is Computerized Tomography (CT). FIG. 5a is an example of a sectional CT image of a toothless mandible 30. Cortical layer 34 (white) encloses trabecular area 36 (gray), which surrounds mandibular canal 38 (black ellipse). FIG. 5b is an example of a toothless maxilla 50. Cortical layer 54 (white) covers trabecular area 56 (gray). Cortical floor 58 (white) borders signal and nasal cavities 60 (black).
A CT image of an upper or lower jaw provides a sectional view of the jaw, and is less distorted than panoramic radiography. However, CT involves a substantially higher dosage of X-ray radiation than conventional radiography, and therefore poses a significantly greater risk to the health of the patient. Furthermore, CT equipment is very expensive and is only rarely found inside the clinic of the implantologist. CT can definitely not provide a chair-side imaging solution.
The popularity of ultrasonic medical diagnostic systems has significantly risen in recent years. In contrast to X-ray and CT systems, ultrasonic systems have the advantage of not exposing the patient or doctor to hazardous ionizing radiation, and are generally more compact and economical. In the field of Dentistry and Dental Implantology various ultrasonic diagnostic and measurement systems are known.
International patent application PCT/IL00/00341 publication no. WO 01/00102 entitled “Alveolar Bone Measurement System” (hereunder “ABMS”), which is fully incorporated herein by reference, discloses an ultrasound system for assessment of distance between an area of interest and a known location of a non-bone canal for use in drilling an implant receiving cavity in the alveolar bone of a human subject's posterior mandible or posterior maxilla. ABMS comprises an ultrasound probe capable of being introduced at the area of interest and transceiving pulse echo ultrasound signal to the alveolar bone and therefrom and an electronic circuitry for processing the ultrasound signal and providing an indication of the remaining alveolar bone distance between the ultrasound probe and a canal within the alveolar bone.
However, ABMS still comes short of answering the needs of the dental implantologist for the following reasons. First, measurement of time-of-flight (TOF) from a location on the surface of the alveolar bone to a non-bone canal inside the jaw is, in reality, impracticable or at least very imprecise due to the high level of attenuation and scattering inside the jawbone. Although the application further discloses an improved method in which a second TOF measurement is taken after drilling a bore of known depth, the improvement is still subject to the aforementioned attenuation and scattering problem, and moreover, as mentioned in the ABMS patent application itself (page 2 line 1) it is of significance that the condition of the jaw be assessed prior to drilling. Second, ABMS relies on the so-called “average velocity of ultrasound within bone tissue, as known, per se” (page 4, line 14). However, it is known that the velocity of ultrasound may vary from patient to patient, and from bone to bone within a certain patient, and even in different regions of a certain bone. Thus, even in the case that ABMS manages to take a precise TOF measurement, it will still not be able to calculate the precise distance from the probe to the canal due to an error in the velocity of ultrasound. Third, ABMS does not disclose any mechanism or procedure for ensuring that the echo which is supposedly from the canal and on which the distance measurement is based, is really from the canal and not from another reflector inside the jawbone. Fourth, ABMS is limited to measuring the distance from the canal to the alveolar bone, and does not teach how to measure the distance between the canal and the buccal and lingual walls of the jawbone, which is of significant importance to the implantologist, e.g. in order to determine an optimal angle of drilling. Lastly, being a measurement system rather than an imaging system, the most ABMS can provide is a numerical distance measurement from the location where the probe is located to a canal within the bone, but no implantologist will suffice with a mere numerical value as a basis for planning or performing a drill into a jaw.
German Patent No. DE 19921279 (hereunder “the '279 patent”), which is fully incorporated herein by reference, discloses a surgical instrument for drilling into a bone, the instrument comprising an ultrasonic transducer for transmitting and receiving ultrasonic waves. The transducer is connected to a device which generates signals according to the intensity and TOF of ultrasonic energy received by the transducer, and these signals provide measurements for determining the characteristics of the bone in the direction of transmission. The '279 patent suffers from limitations similar to those of ABMS, namely, impracticable or imprecise measurement and insufficient information to the implantologist.
U.S. Pat. No. 6,030,221 entitled “Ultrasonic Apparatus and for Precisely Locating Cavitations within Jawbones and the Like” (hereunder “the '221 patent”), which is fully incorporated herein by reference, discloses an apparatus which generates an ultrasonic pulse and passes the pulse through the jawbone of a human. The pulse is detected by an ultrasonic receiving unit. Attenuations in the amplitude of the pulse are detected and displayed on a color monitor. The color monitor allows the detection of cavitations by interpreting color codes in a 4×4 matrix displayed oil the monitor.
U.S. Pat. No. 6,086,538 entitled “Methods and Apparatus for Evaluation of Bone Condition” (hereunder “the '538 patent”) discloses a method of evaluating the status of bone tissue, useful in the diagnosis of osteoporosis, in which a calcaneus is scanned in through-transmission mode, and a characteristic of ultrasound, such as the speed-of-sound or attenuation, is measured in different locations. The location of a circular (as seen from the side) area of reduced attenuation inside the calcaneus is derived from the ultrasound measurements, and finally the status of the examined bone tissue is evaluated based on the measurements which were taken in that circular area.
Both the '221 patent and the '538 patent concentrate on the problem of assessing the quality or health of the bone under examination rather than providing an image of the bone for guidance in a medical procedure. As a result, both these patents provide only a two-dimensional attenuation map of the examined bone which is perpendicular to a cross-section of the bone, and furthermore, include no mechanism or procedure for precisely calculating the distance of the detected cavitations (in the case of the '221 patent) or the circular area of reduced attenuation (in the case of the '538 patent) in relation to a reference point of interest. As mentioned hereinabove in connection to the panoramic X-ray technique, a lateral two-dimensional image is unreliable for guiding the implantologist to drill within the bone boundaries and within a safe distance from the mandibular canal, or the signal/nasal cavities.
German Patent No. DE 4205360 (hereunder “the '360 patent”), which is fully incorporated herein by reference, discloses an ultrasonic measuring gauge for determining jawbone width. U.S. Pat. No. 5,427,105 entitled “Measuring Procedure for the Thickness of the Mucous Membrane of an Alveolar Process” (hereunder “the '105 patent”), which is fully incorporated herein by reference, discloses an ultrasonic method for measuring the thickness of the mucous membrane in the region of the jawbone ridge. Neither the '360 patent nor the '105 patent comprise any mechanism for scanning the bone being examined. Neither patent provides an image of the bone, nor any information regarding the internal structure of the examined jawbone.
U.S. Pat. No. 5,564,423 entitled “Ultrasonic Measurement System for the Determination of Bone Density and Structure” (hereunder “the '423 patent”), which is fully incorporated herein by reference, discloses an electronic system for measuring the density and structure of bone, equipped with ultrasonic calipers designed to be applied to a segment of the human body (for example, a finger) containing bone tissue to be examined. The ultrasonic calipers include a transmitting transducer and a receiving transducer, which enable measuring TOF in the bone tissue based on a through-transmission method. The system provides an indication of the density and structure of the bone tissue based on the measured TOF. Since the '423 patent relies on TOF measurement, it suffers from the same impracticability and inaccuracy problems mentioned above in connection to ABMS. Likewise, the '423 patent also does not comprise any mechanism for scanning the examined bone tissue, and does not provide the location and image of internal structures within the bone tissue.
Thus, none of the above solutions provides an economic, radiation free, real-time, chair-side imaging tool to the implantologist. Ongoing monitoring of the drilling process allows for depth and angulation corrections on the fly. There is thus a widely recognized need for, and it would be highly advantageous to have systems for ultrasonic imaging of a jaw, methods of use thereof and coupling cushions suited for use in the mouth devoid of the above limitations.